The overwhelming dominance of privately-educated schoolchildren in Britain is
“corrosive” for society, Nick Clegg has warned.

The sheer gulf in standards between state and independent schools is holding back social mobility and damaging the economy, according to the Deputy Prime Minister.

He said children educated in the private sector were three times more likely to achieve at least two As and B at A-level – the entry requirement for many top research universities – than pupils in state schools.

The gap in results between different school types is wider in Britain than almost any other developed country, it was revealed.

The comments were made as he prepared to launch a new drive designed to boost standards among poor children.

On Tuesday, the Government will unveil a list of “social mobility indicators” designed to track the progress of deprived pupils – guiding future policy decisions on education, health and employment.

Speaking ahead of the announcement, Mr Clegg, who attended fee-paying Westminster School in central London, said education was “critical to our hopes of a fairer society”.

But he added: “Right now there is a great rift in our education system between our best schools, most of which are private, and the schools ordinary families rely on.

“That is corrosive for our society and damaging to our economy.

“I don’t for a moment denigrate the decision of any parent to do their best for their child, and to choose the best school for them. Indeed, that aspiration on behalf of children is one of the most precious ingredients of parenthood.

“But we do need to ensure that our school system as a whole promotes fairness and mobility.”

The comments come just weeks after Michael Gove, the Education Secretary, said levels of social stratification in British schools were “morally indefensible”.

He said public schools were already significantly over-represented in politics, the judiciary, banking and FTSE 100 boardrooms.

But Mr Gove insisted there was also evidence of the creeping influence of independent education on industries dominated by young adults in their late teens and 20s, including acting, sport, comedy and music.

Some seven per cent of state school students achieved AAB at A-level in 2011, compared with 23.1 per cent among pupils from the independent sector, figures show.

International research reveals that the gap in attainment between teenagers from state and private schools is now the fourth biggest in the world.

In a speech to the Sutton Trust charity on Tuesday, Mr Clegg will outline plans for a new set of indicators to measure the impact of Government policies designed to improve social mobility. This includes assessing the number of poor children who go on to gain good A-levels.

It comes on top of the introduction of the “pupil premium” – a cash bonus for schools teaching poor children. This year, head teachers received £488 for each child eligible for free school meals, rising to £600 in 2012/13.